First off - when shooting through glass you'll end up with distortion in your shots unless you put the lens parallel to the glass and shoot through it - also it helps to get as close to the glass as you can to avoid glare/reflections and also make sure your glass is clean!
Generally a tripod is ideal to reduce camera shake (when shooting corals I used to set the tripod up and use the cameras self timer so that I wasn't shaking the camera by pushing the shutter button) also try to avoid using the digital zoom (stick with your 3x optical zoom)
The camera does have a macro mode (probably a little green flower icon on the dial on the top) try using that - it might allow you to get closer to the glass to shoot
You can also try finding a clear drinking glass with a distortion free bottom that you can try shooting top down shots through (stick bottom of glass below the surface of the water and then shoot THROUGH the glass - think like a glass bottom boat!)
Hrmmmmm otherwise it's practice practice practice
the beauty of digital is you can always delete the crappy shots
Feel free to ask any more questions
I may not know everything but I can try and help!
EDIT: some light reading materials for you too! http://blog.gregdisch.com/2009/07/26...blic-aquarium/ http://blog.fotonomy.com/tips/8-tips...uarium-photos/